The use of and advantages associated with portable computers are well known in the art. Over the last decade, there has been an intense effort in the computer industry to down size the personal computer ("PC") to provide users with a powerful yet portable computer that can be taken out of the office and fully utilized at home or on the road. As advancements have been made in both microprocessing chip and battery technologies, particularly over the last decade, PCs were eventually downsized into "laptop computers". While these computers offered the portability and processing power of a full sized PC, the laptop was still somewhat large and heavy for the user to carry around. In response to these disadvantages, the laptops were downsized even further into what is now commonly known in the industry as a notebook computer, which is smaller and more light weight yet possessing equal or greater processing capabilities than their earlier laptop counterpart.
Because of their portability, notebook computers are frequently used in various places that require the user to operate the notebook computer from their lap, hence their name for their earlier counterpart. In such instances, the user must type with his or her wrists bent upwardly at an unnatural angle. This can lead to or exacerbate any pre-existing condition resulting from prolonged typing operations, such as tunnel carpel syndrome ("CTS") or other typing-related injury that the user may have.
CTS has become a major problem with respect to individuals who do extensive amounts of typing during their typical work day. CTS is caused by cumulative damage to the finger tendons as they pass through a two to three centimeter (2-3 cm) long, narrow, rigid channel in the wrist, the carpal tunnel. With the hand oriented palm down, the roof of the carpal runnel is formed by the arch of the carpal bones and the floor by the tough transverse carpal ligament. The carpal tunnel contains the tendons for the fingers, the radial artery, and the median nerve which transmits sensation for the thumb and the first 2.5 fingers. Sensation for the remaining 1.5 digits is transmitted via the ulnar nerve which runs outside of the carpal tunnel.
As the hand deviates from normal either (i) horizontally either towards the thumb (radial deviation) or towards the little finger (ulnar deviation), or (ii) vertically up or down; the pressure on the carpal tunnel increases. Vertical deviations (extension/flexion) create significant increases in carpal tunnel pressure. Accelerations from extension to flexion are thought to pose the greatest risk for CTS, and when the hand is in a wrist neutral position (i.e., no vertical or horizontal deviation) then there is minimum pressure on the tendons and the median nerve in the carpal tunnel. With occupational overuse of the fingers, minor trauma to the tendons and the sheaths may accumulate and eventually produce CTS.
As the tendons or their sheaths become irritated and inflamed, the resulting swelling increases the pressure on the median nerve, which initially causes tingling, then numbness, and eventually disabling pain when the fingers are moved. Computer users are particularly at risk because of the large number of finger movements which the fingers may make in a short time. For example, a data entry worker who averages 13,000 key strokes per hour will make over half-a-million finger movements per week. In short, the three major risk factors for CTS are poor posture, pressure in the carpal tunnel and lack of pauses to allow time for tissue repair.
The use of QWERTY keyboard layouts, which can cause some ulnar deviation of both hands, and a positive keyboard angle which places the hands in an extended posture, combine to increase the risks of CTS. Over time these factors accelerate the accumulation of trauma to the hands/wrists, and this cumulative trauma is now appearing as the epidemic of CTS cases. Also, QWERTY keyboards usually are asymmetrical (i.e., the numeric keyboard is to the right of the QWERTY keys) and users tend to center the keyboard on their screen rather than centering QWERTY on the screen. This can result in users sitting in, twisted postures which increase the risks of back, shoulder and neck problems.
To reiterate, the major contributing factors to the occurrence of CTS are believed to fall primarily within the categories of (i) poor posture, (ii) no or insufficient pauses during work, and (iii) undesirable pressures. "Poor posture" includes (i) wrist extension, (ii) hand deviation, and (iii) poor seated posture. "No or insufficient pauses" include (i) repetitive movements. (ii) no or inadequate micro-breaks, and (iii) impaired tissue repair. "Undesirable pressures" include those pressures resultant from (i) flexion/extension accelerations, (ii) increased carpal tunnel pressure, and (iii) increased tissue trauma.
Because of the significance of the CTS problem, a number of previous products have attempted to reduce CTS risks. First, the layout of data entry keyboards have been modified. Keyboard re-designs to minimize horizontal radial or ulnar deviation have been developed. However, the problem of vertical deviation (extension) remains even with these keyboards. Also, postural risks from using other input devices (e.g., mouse) are obviously unaffected by modification to keyboard layout.
Second, wrist rests have been provided. Each arm weighs about 2.5% of a human's total body weight. The ability to rest the wrists on a support helps to reduce muscular activity in the forearm and incidentally reduce pressure in the carpal tunnel. However, problems of flexion/extension and ulnar/radial deviation remain because of the design and slope of the keyboard. Moreover, wrist rests defeat the portability aspect of notebook computers since the notebook computer is designed to be light-weight and as peripheral- component-free as possible.
Third, full motion fore-arm supports have been provided. These products provide full motion fore-arm support for the worker. Each arm is rested in a mobile support which takes the arm weight for all horizontal movements. However, as with wrist rests, problems of flexion/extension and ulnar/radial deviation remain because of the design and angle of the keyboard, and in a short-term test the use of full motion fore-arm supports resulted in a slight slowing of typing speed. Again, these devices are not well suited for portable applications because they affect the portability aspects of the computer.
Accordingly, there is a need in the art for a portable computer that has an adjustable palm rest integrated into the chassis of the portable computer to allow the user to achieve a wrist-neutral position (i.e. where the wrist is substantially level with the palm) and thereby reduce the risk of CTS injury. In addition, the angle of the adjustable palm rest's orientation with respect to the plane of the keyboard can vary with different working environmental situations. The present invention provides a portable computer that addresses these needs.